1. Field of the Invention
The present invention relates to a heat exchanger for generating hot water by heat recovery from combustion gas generated by a burner, for example. The invention also relates to a water heater provided with such a heat exchanger.
2. Description of the Related Art
For example, a conventional heat exchanger includes a casing into which combustion gas is to be introduced and a plurality of heat transfer tubes arranged in the casing. A water inflow header and a hot-water outflow header are connected to the heat transfer tubes. (See Japanese laid-open utility model publication No. 57-200853, Japanese laid-open utility model publication No. 64-12151 and Japanese examined utility model publication No. 4-22216, for example.)
With this structure, when water is supplied to the water inflow header, the water flows into the plurality of heat transfer tubes and is heated while flowing through the tubes. The hot water produced in this way merges at the hot-water outflow header and is supplied from the header to the intended faucet or place. The plurality of heat transfer tubes provide a plurality of water flow paths arranged in parallel with each other. With this structure, as compared with the structure in which only a single water flow path is provided, the length of each water flow path can be shortened, so that the water pressure drop in the water flow process can be reduced. Therefore, the heat exchanger is usable even under the conditions in which the water pressure in supplying water to each of the heat transfer tubes is low.
However, the above-described conventional structure has the following drawbacks.
Generally, the header is connected to the heat transfer tubes by welding or brazing. In this case, however, it is difficult to detach the header from the heat transfer tubes. Therefore, when the heat transfer tube is clogged, the repair of the heat transfer tube in the state detached from the header is difficult. In this way, the conventional structure is inconvenient for maintenance.
The structure disclosed in Japanese laid-open utility model publication No. 57-200853 includes a header provided with a plurality of relatively short joint tubes. By fitting the joint tubes to the ends of the heat transfer tubes, the header is connected to the heat transfer tubes. With this structure, the joint tubes and the heat transfer tubes can be detachably connected to each other without performing welding or brazing. Therefore, the inconvenience for maintenance is removed.
However, the parts of the heat exchanger may include a dimensional error. Specifically, for example, in manufacturing a heat exchanger, through-holes are formed at a wall of the casing. The heat transfer tubes are inserted into the through-holes and then bonded to the casing by performing welding with respect to the portions around the through-holes. However, this method often causes a relatively large dimensional error in the arrangement of the ends of the plurality of heat transfer tubes. Further, an error in the arrangement is often caused in providing a plurality of joint tubes at a header. When the arrangement of the heat transfer tubes and the joint tubes of the header include such dimensional errors, it is difficult to properly fit the heat transfer tubes to the joint tubes, so that the proper connection may not be performed.